Conventionally, there has been proposed plasma processing to apply processing, for example, CVD processing, etching processing, and the like, to a substrate in a process vessel by generating plasma in the process vessel through the use of a microwave.
A conventional plasma processing apparatus of this type using a microwave has a flat plate-shaped transmissive window made of a dielectric, for example, quartz or ceramics, to cover an upper opening of a process vessel, and in the process vessel, this transmissive window is supported by a support part supporting a peripheral edge portion of the transmissive window. On an upper face of the transmissive window, provided is a metal plate called, for example, a slot antenna, on which a large number of slots or slits are formed. The microwave is supplied to an area above the dielectric and the microwave leaking from the slots or slits generate an electric field under the transmissive window, so that process gas introduced into the process vessel turns into plasma, whereby predetermined plasma processing is performed (see Patent document 1).
However, in the method of generating the plasma by the microwave excitation as described above, a strong electromagnetic field standing wave is formed in the transmissive window, so that high-energy plasma by a strong electric field tends to be formed (here, referred to as “an edge effect”) especially in a contact point between the transmissive window and the support part supporting the transmissive window (for example, in a peripheral edge portion of the support part on an inner side of the process vessel). This is because in an area near the dielectric, a microwave electric field is strong and thus electron temperature of the plasma gets higher, and if a surface of an object exists in this area, a potential difference increases to heighten irradiation energy of ions to this surface.
As a result, a member near the aforesaid contact point is sputtered by the plasma to adhere to a substrate being a processing target, which may possibly cause nonuniformity in processing rate of the processing target and deteriorate processing quality. Further, near the contact point, quality (for example, radical density, plasma density, or electron temperature) of plasma becomes different from quality of plasma generated in other portions of the transmissive window, which may possibly lead to nonuniform processing. Such a phenomenon becomes more distinguished in a case where power is increased for high-speed processing.
[Patent document 1] Japanese Patent Application Laid-open No. 2002-299240